In medical practice, an affected part in internal organs, skeletons, and the like is photographed with, for example, X-rays for various tests and diagnoses. Through application of recent digital technology, a moving image (an image group composed of a plurality of frame images) that captures the movement of an affected part with X-rays or the like can be acquired relatively readily.
In the recent digital technology, a dynamic image of a subject region including a diagnosis target region can be photographed using a semiconductor image sensor such as a flat panel detector (FPD), enabling diagnosis through motion analysis of the diagnosis target region, which cannot be made in still image photographing and diagnosis by conventional X-ray photography. Particularly in dynamic analysis of the chest with X-rays, the use of interframe differences of a moving image in the chest enables analysis of a ventilatory function and a blood flow function related to two major movements, namely, respiration and heart rate, for every position of the chest. Such analysis therefore receives attention as the method of readily diagnosing respiration and blood flow with a small amount of exposure.
In recent years, various image processing technologies have been proposed as dynamic analysis of the ventilatory function and the blood flow function. For example, Patent Document 1 discloses the following technology. Filters are separately used in such a manner that the processing using a highpass filter is performed in blood flow analysis and the processing using a lowpass filter is performed in ventilatory analysis to prevent the blood flow and respiration from affecting each other and prevent the density values thereof from affecting each other, thereby accurately extracting the respiration and blood flow using an inter-filter difference.
Patent Document 2 discloses a technology of detecting a current phase in a respiratory cycle of a test subject to control an X-ray source in accordance with the current phase.
Pathological analysis and diagnosis based on a motion analysis for a diagnosis target region, which cannot be performed through still image photographing and diagnosis based on the conventional X-ray photographing, are tried using a semiconductor image sensor such as an FPD described above. Particularly in dynamic analysis of the chest using X-rays, the following study is conducted; the respiratory information and blood flow information in the lung field are extracted, and the dynamic function as to changes in the density value of the lung field and the movement of blood flow at every position are quantitively analyzed, to thereby aid diagnosis and/or treatment (CAD for X-ray moving image).
As the method for the quantitative analysis as described above, the following methods for ventilatory analysis and blood flow analysis are proposed. Such a method analyzes temporal changes on the basis of the interframe difference information of a moving image of the chest to acquire detailed functional data for every position of the chest, that is, the information on the abnormal-ventilation-spot analysis values regarding the movement in respiration and on the abnormal-blood-flow-spot analysis values regarding the movement of a blood flow.
For example, Patent Document 3 discloses a technology of calculating differential images of temporally adjacent images using a plurality of X-ray moving images acquired continuously in time sequence, thereby generating one image composed of pixels each indicating a maximum pixel value for its corresponding pixel group in a plurality of differential images.
Patent Document 4 discloses a technology of using the property, in which the pixel value of the lung field in an X-ray image of the chest changes due to cardiac pulsation, and employing the information on changes in pixel value as the information on pulmonary blood flow, thereby effectively using the information for diagnosis of pulmonary embolism, cardiac disease, or the like. In a specific technique for the method, the dynamic state of the heart during ventricular dilation is acquired to generate the information on changes in the pixel value of the X-ray moving image of the chest associated with an increase in blood flow (an increase in pulmonary blood flow) from the heart to the lung during ventricular contraction.
Patent Document 1 described above further discloses a technology of separately using filters in such a manner that the processing using a highpass filter is performed in blood flow analysis and the processing using a lowpass filter is performed in ventilatory analysis to prevent the blood flow and respiration from affecting each other and prevent the density values thereof from affecting each other, thereby accurately extracting respiration and blood flow using an inter-filter difference.